00:01
First, we recognize that with the addition of sodium hydroxide, the hydroxide of sodium hydroxide is going to react with the formic acid, which i'll represent as ha, and create more formate and water.
00:16
Every mole of hydroxide we add consumes the mole of formic acid and makes the mole of formate.
00:21
As long as we don't add more hydroxide than we have formic acid, we'll still have ha and its conjugate base, so we will still have a buffer solution.
00:32
For buffer solutions, we can calculate ph using the henderson -hasselbalch equation, where ph is equal to pka plus the log of the moles of the base over the moles of the acid.
00:46
Now i know a lot of people will use a ratio of molarity here rather than a ratio of moles, but a ratio of moles is equivalent and it makes the calculation easier.
00:57
Then we don't need to worry about volume.
01:00
We don't ignore the fact that the volume changes, it just doesn't matter with the calculation anymore.
01:07
So ph will be equal to pka, which will be the negative log of the ka value for formic acid, 1 .8 times 10 to the negative 4.
01:19
We then add to that the log of the moles of formate...